Should I Deadhead My Bearded Irises?

Hardy in U.S. Department of Agriculture plant hardiness zones 3 to 9, irises (Iris spp.) are easy perennials to grow and maintain. Bearded irises (Iris germanica) get their name from the short, fuzzy filaments on the flowers' three downward-hanging petals, known as falls. Deadheading irises ‒ removing faded flowers from the plant ‒ is necessary to keep the plants looking and performing their best.

Bearded irises are divided into six groups based on height. They range from tall bearded irises, which have an average height of 3 feet and are the most common, to miniature dwarf bearded irises, which can be as short as 8 inches. In the middle are intermediate bearded irises, with a height between 16 and 28 inches. Intermediate varieties are often used in bouquets.

The smallest irises bloom the earliest. Some varieties of tall bearded iris are reblooming, which means they produce flowers for a second time in the fall. While blue and purple irises varieties are perhaps the best known, hybridization has produced bearded irises in warm colors, such as red, yellow and orange. There are also white irises from which to choose, while others are bicolored.

Bearded irises grow best in slightly alkaline soil, which means a pH just about 7.0, and they can tolerate a variety of soils as long as drainage is adequate. As a rule of thumb, bearded iris rhizomes ‒ the fleshy underground roots from which the plants draw energy ‒ should be planted 18 inches apart, adding or taking away a few inches depending on the size of the cultivar. Bearded irises require between six and eight hours of sun per day to perform well.

Irises will benefit from a low-nitrogen fertilizer, though you will need to make sure that the fertilizer does not come in contact with the rhizome. Also be cautious when applying mulch to bearded irises, as it can encourage root rot. In cold climates where irises will need winter protection, use a lightweight material, such as straw, to keep the rhizomes from heaving out of the ground as it freezes and thaws. Bearded iris rhizomes become crowded and must be divided every three to four years.

Deadhead iris blooms as soon as they fade and not just because they look unattractive. If they are left on the plant, the flowers will form seed pods, a process that takes energy away from other parts of the plant. If allowed to disperse, iris seedlings will also crowd the soil around the mother plant. In the case of reblooming irises, deadhead faded flowers immediately to allow the plant enough time to produce new blooms in the fall.

When deadheading iris plants, leave any unopened buds and green leaves on the plant. To prevent diseases on the leaves of the iris plant from overwintering, remove and discard all of the foliage in the fall when the leaves have turned brown. Cut the plants down to 1 or 2 inches above the ground after the first frost of autumn.